**Core Concept**
The question is testing the understanding of the mechanism of injury and common patterns of lower limb fractures in the elderly. **Hip fractures**, specifically **extracapsular fractures** such as **intertrochanteric fractures**, are common in this age group due to osteoporosis and falls.

**Why the Correct Answer is Right**
The mechanism of injury described, with the lower limb extended and externally rotated, is consistent with an **extracapsular hip fracture**. When a person falls and lands on a flexed hip, the force of the impact causes the femoral neck to break, often resulting in an **intertrochanteric fracture**. This type of fracture is more common in the elderly due to osteoporosis, which weakens the bone and makes it more susceptible to fractures.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not mentioned.
* **Option B:** This option is not mentioned.
* **Option C:** This option is not mentioned.
* **Option D:** This option is not mentioned.

**Clinical Pearl / High-Yield Fact**
In the elderly, a person who falls and experiences pain in the hip or groin area should be suspected of having a hip fracture, and an X-ray should be ordered promptly to confirm the diagnosis.

**Correct Answer:** C. Intertrochanteric fracture